Research

Direct assessment of the release of fixed nitrogen in the rhizosphere of pea, lentil, chickpea, and faba bean

Chickpeas

Faba Beans

Lentils

Peas

Crop Rotation

Soil Health

Sustainability

University of Saskatchewan

Lead Investigator(s)

Dr. Richard Farrell

Lead Investigator(s) Institution

University of Saskatchewan - Dept. of Soil Sciences

Objective

To determine N2 fixation in lentil, pea, chickpea, and faba bean using continuous 15N2 labeling. To determine the release of fixed-N into the rhizosphere of mature lentil, pea, chickpea, and faba bean. To quantify the supply of fixed-N from the pulse crop residues to the N uptake of a subsequent cereal crop (wheat). To assess the N2O emissions from soils containing pulse vs. wheat residues and identify the source of soil-emitted N2O.

Outcome

In terms of above-ground biomass, biological nitrogen fixation (BNF) was greatest for faba bean and chickpea, intermediate for lentil, and lowest for pea. It was determined that poor nodulation of the pea resulted in the low BNF values, hence pea was not included in the wheat phase of the study. On a whole-plant basis, BNF was greatest for chickpea, intermediate for faba bean and lentil, and lowest for pea. During the wheat phase of the study, we determined that grain yield was about 30% greater for wheat on pulse residue compared to wheat on wheat residue. The results further suggest that nitrogen (N) in lentil was more readily available than that in the other pulses, presumably reflecting differences in the quality of the pulse residues. The results lend support to the argument that, in terms of nitrious oxide (N20) emissions, residue-N is not equivalent to fertilizer-N, and that accurate accounting of both the N-credit and N-penalty associated with the decomposition of pulse crop residues deserves more attention. Demonstrating that pulse crop residues have low N2O emissions also should serve as a marketing tool for the Pulse Industry as consumers become increasingly aware of “carbon footprints” associated with different products.